1. Field of the Invention
This invention relates to a semiconductor memory circuit, and particularly to a selection circuit for outputting a select signal indicative of an address for a redundancy memory cell (or a memory block with redundancy memory cells placed therein).
2. Description of the Related Art
A semiconductor memory circuit has a plurality of memory cells for respectively storing data therein. This type of semiconductor memory circuit is formed on a semiconductor substrate. With an increase in memory capacity and an improvement in integration density, the number of memory cells included in one semiconductor memory circuit becomes massive. Defective memory cells cannot be prevented from occurring in a process for fabricating a semiconductor memory circuit. Thus, a method of forming redundancy memory cells in a semiconductor memory circuit in advance in view of the occurrence of defective memory cells is now adopted. A semiconductor memory circuit formed on a semiconductor wafer is first examined or tested in a wafer state. If any defective memory cell is found, then a redundancy relieving process is executed so as not to select the defective memory cell and to select a redundancy memory cell (or a memory block with redundancy memory cells placed therein) as an alternative to the defective memory cell. Since an address for the defective memory cell is unspecified, a selection circuit is used which has fuses and sets an address for each redundancy memory cell. Selecting the corresponding redundancy memory cell is achieved by cutting a specific fuse provided within the selection circuit.
However, current flows from a source potential to a ground potential through the corresponding fuse depending on the placement of the fuses in the selection circuit, so that power to be used up by the semiconductor memory circuit increases. The more the number of redundancy memory cells increases, the more the number of fuses becomes great. Thus, since power to be consumed by a semiconductor memory circuit also increases, there has been a demand for improvements in such disadvantages.